Protective device for galvanic cells

ABSTRACT

A protective device for galvanic cells ( 201, 202, 301, 302 ) which are interconnected via contact elements ( 205, 207, 209, 212, 405, 409, 406, 407, 506, 507, 509, 606, 607, 706, 707, 709, 805, 806, 807, 809 ) that are suitably connected to pole connections ( 203, 204, 503, 504 ) of said cells to give a battery can be associated with individual cells of a battery. The protective device has an activation device ( 1008, 1108, 1208, 1011, 1111 ) for activation. When the protective device is activated, the protective device bridges the cell associated therewith by changing the interconnection and thus removes it from the electrical functioning of the battery assembly. In the activation device, preferably an electroconductive or insulating component made of a shape memory material brings about the change of the interconnection by changing the shape of said component as soon as and/or as long as the temperature of said component lies outside a defined temperature range.

The invention relates to a protective apparatus for galvanic cells, agalvanic cell with a protective apparatus of this type and a batterymade up of such galvanic cells.

Batteries consist of individual cells connected in series and/or inparallel, which are often located in a common housing with theassociated electronics and cooling. In automotive technology, batteriesof this type, in particular high-voltage batteries are used inter aliaas traction battery for electric vehicles and as energy buffer storageunit for hybrid vehicles. Cells of this type can be damaged, forexample, by overcharging, by short circuit or due to other causes, orotherwise disrupted in terms of their intended function.

For example, lithium-ion batteries are known, which interrupt thecircuit when the cells are overloaded or short circuited. It is knownfor example, in the case of overheating of a cell of this type, to breakopen the housing thereof at a targetedly weakened point, for examplewith the aid of a rupture disc, under the action of the simultaneouslyincreased internal pressure of the cell, and in this case, to separatethe electrical contact of the electrode winding to the battery poles.Known solutions of this type are in some cases connected with thedisadvantage that, due to the cell-side disconnection of the circuit,the cells connected in series to the defective cell can likewise nolonger emit current. Particularly in the case of electric vehicles, thiscan lead to total failure (“dead vehicle”). In the case of hybridvehicles, depending on the system structure, the restarting of theinternal combustion engine may for example no longer be possible.

To prevent these disadvantages, apparatuses have been suggested, inwhich a defective cell is removed from the electric series connectionand is bridged at the same time. In the case of such known solutions,the device for cell-side disconnection of the circuit and for bridgingthe defective cell often obtains its actuation energy from the pressureincrease in the interior of the cell. These known apparatuses aretherefore only effective if the cell is already irreversibly damaged. Insuch cases, the cell contents, for example a partially evaporatedelectrolyte, can escape, which can cause further short circuits due toits electrical conductivity. Repairing the battery is often no longerpossible or worthwhile in such cases, because the interior of thebattery is attacked within a short time due to the corrosive action ofthe electrolyte.

The present invention is based on the object of specifying an effectiveprotective apparatus for galvanic cells and, if possible, avoiding theproblems connected with the known solutions.

This object is achieved by means of a protective apparatus for galvaniccells according to claim 1. It is further achieved by means of anarticle according to one of the further independent claims.

The invention provides a protective apparatus for galvanic cells whichare interconnected to form a battery by means of contact elementsconnected to pole connections of the cells in a suitable manner. Theprotective apparatus according to the invention is characterised in thatit has an activation apparatus for activating the protective apparatus.This protective apparatus according to the invention bridges a cellassigned to it by means of a change of the interconnection in the caseof an activation of the protective apparatus and thus electricallyremoves this cell from the battery assembly.

Terms used in connection with the description of the present inventionare defined and explained in the following.

A galvanic cell in the sense of the present invention should beunderstood as meaning an electrical or electrochemical cell suitable forconstructing a battery, in particular a primary cell or a secondarycell. Cells of this type are also designated as battery cells, cells orindividual cells in the following. A battery is to be understood asmeaning an interconnection of cells of this type in series and/or inparallel.

An interconnection of galvanic cells is to be understood in connectionwith the present invention as meaning any technically sensiblecombination of series and/or parallel connections of cells of this type.It is produced by means of suitable connection of the pole connectionsof such galvanic cells with the aid of contact elements, particularlywith the aid of contact plates, contact rails, insulators, etc.

In the present context, an activation apparatus is to be understood asmeaning any apparatus for activating the protective apparatus accordingto the invention, which puts a protective apparatus according to theinvention into a position to bridge individual cells of a battery in atargeted manner and thus to electrically remove the same from thebattery assembly. The expression electrically remove means that althoughthe respective cell spatially remains at its position in the batteryassembly, this cell is removed from the electrical series and/orparallel connection of a plurality of cells, which constitutes thebattery, by means of the bridging of certain contacts.

Energy is required to activate the protective apparatus with the aid ofthe activation apparatus, for example because contact elements must bemoved to this end. According to the invention, this energy is fed to theactivation apparatus from outside or provided by means of an energystore which is a constituent of the protective apparatus or theactivation apparatus. Here, one may be concerned with energy stores ofany possible type, particularly mechanical energy stores. In the case ofthe feeding of the energy required for activation from outside, any typeof suitable apparatus comes into consideration, particularlyelectromagnetic converters such as for example electromagnetic switches(relays, etc.), which are operated with the aid of energy which is fedfrom outside, that is to say for example is withdrawn from the batteryassembly, the remaining cells of which remain regularly functional.

Advantageous developments of the invention form the subject ofsubclaims.

In the following, the invention is explained in more detail on the basisof preferred exemplary embodiments and with the aid of figures. In thefigures

FIG. 1 a shows a circuit diagram of a series connection of battery cellswhich in each case have an actively controllable cell-side apparatus forremoving and for bridging cells electrically connected in seriesaccording to a preferred embodiment of the invention;

FIG. 1 b shows an interconnection of battery cells with the switches ofa protective apparatus, in which all switches are in a position whicheffects a series connection of all of the battery cells;

FIG. 1 c shows an interconnection of battery cells, in which one switchis in a position which effects a bridging of a battery cell and thus theremoval thereof from the battery assembly;

FIG. 2: shows an interconnection of battery cells with protectiveapparatuses according to a preferred embodiment of the invention;

FIG. 3: shows a side view of a cell block with protective apparatusesaccording to a preferred embodiment of the present invention;

FIG. 4 shows an enlarged illustration of the upper part of the cellblock illustrated in FIG. 3 with a protective apparatus according to apreferred embodiment of the present invention;

FIG. 5 shows the view of a cell with a protective apparatus according toa preferred exemplary embodiment of the present invention;

FIG. 6 shows a detailed view of a protective apparatus according to apreferred embodiment of the invention;

FIG. 7 shows an exploded illustration of the embodiment shown in FIG. 6;

FIG. 8 shows a side view of a protective apparatus according to apreferred embodiment of the invention in the inactive state (normaloperation);

FIG. 9 a shows a sectional image of a protective apparatus according toa preferred embodiment of the invention;

FIG. 9 b shows an enlargement of the right part of the embodiment shownin FIG. 9 a in the inactive state (normal operation);

FIG. 10 shows the view of a cell block with activated protectiveapparatus according to a preferred embodiment of the present invention;

FIG. 11 shows a side view of an activated protective apparatus accordingto a preferred embodiment of the present invention;

FIG. 12 a shows a sectional image of a protective apparatus according toa preferred embodiment of the invention in the case of an activatedprotective apparatus; and

FIG. 12 b shows an enlarged illustration of the right part of theembodiment of an activated protective apparatus shown in FIG. 12 a.

As illustrated in FIG. 1 a, the fundamental mode of action of aprotective apparatus according to the invention is to remove a defectivecell from an interconnection of a plurality of cells in a targetedmanner by means of bridging. To this end, bridges 104, 105, 106 areprovided, which, in the case of activation of one of the switches 101,102, 103, connect an electrode 107 to the similar electrode of anadjacent cell. In the inactive state of the protective apparatus, bycontrast, the electrode 108 is connected to the dissimilar electrode ofthe adjacent cell. Similarly, FIGS. 1 b and 1 c show the fundamentalmode of action of the protective apparatus according to the invention.As all of the switches S1 b, S2 b, . . . , S5 b in FIG. 1 b are in acorrespondingly similar position, a series connection of cells Z1 b, Z2b, Z5 b is present in FIG. 1 b. In FIG. 1 c, the switch S2 c is in theactivated position, as a result of which, the cell Z2 c is removed fromthe interconnection.

As illustrated in FIG. 2, the interconnection of battery cells takesplace with the aid of contact elements. The contact rails 205, 209 and212 illustrated in FIG. 2 are examples of such contact elements. Theelectrodes (diverters) 203 and 204 are connected or not connected tothese contact elements in a suitable manner. The protective apparatusaccording to the invention is preferably arranged between thestrip-shaped poles (“diverters”) of two adjacent cells in each case. Theactuation energy for the activation of the protective apparatus is forexample stored in a wave spring 208, which is held in its initialposition by a fuse wire 711, 811, 911 shown in FIGS. 7 and 9. At theonset of malfunction, this fuse wire fuses by means of a current pulseand the wave spring 208, 708, 908 shown in FIGS. 2, 7 and 9 lifts thecontact rail hitherto undertaking the electrical series connection andpresses the same against a second contact rail, which electricallybypasses the defective cell.

According to a preferred embodiment of the present invention, theprotective apparatus according to the invention is equipped with anenergy store which stores and in the case of an activation provides theenergy required to change the interconnection. This may be a mechanicalenergy store or other energy stores, chemical or electrical energystores for example. A simply structured energy store 208, 408, 508, 608,708, 808, 908, 1008, 1008, 1108, 1208 is shown in FIGS. 2, 4, 5, 6, 7,8, 9, 10, 11 and 12. A wave spring 208, 408, 508, 608, 708, 808, 908,1008, 1008, 1108, 1208 is held from below by means of a bearing 210,310, 910, 1010, 1110. A fuse wire 711, 811, 911, 1111 holds this wavespring in its initial position and initial shape, that is to say in thetensioned state. If the wire fuses, the wave spring lifts the contactplate 207, 407, 507, 607, 707, 807, 907, 1007, 1207 and presses itagainst the contact rail 1105, 1205. The contact to the contact plate1106 is interrupted. Thus, the bridging of the cell has taken place.

The protective apparatus is preferably located in a housing which is notillustrated in the figures. This housing is preferably closed in anairtight manner to prevent corrosion and, if required, filled with aninert protective gas.

The protective apparatus according to the invention can preferably becontrolled actively and individually for each cell and thus individuallyremove the respective damaged cell from the circuit and bridge the same.If, for example the battery electronics detect the onset of malfunctionby means of the monitoring of the cell voltage and/or the celltemperature, the apparatus can be triggered preventatively. The batteryremains operational with only a slightly reduced voltage level.

The solutions according to the invention, in which the energy foractivation is not withdrawn from a process which is associated with themalfunction or with the destruction of the affected cell which is to bebridged, but rather in which the energy for activation is supplied fromoutside of the protective apparatus or is withdrawn from an energy storewhich is preferably a constituent of the protective apparatus or theactivating apparatus, are connected with the advantage that a cellaffected by a malfunction can already be electrically removed from thebattery assembly at an earlier time, at which the destruction of thecell has not yet begun or even is so far advanced that the energyrequired for activating the protective apparatus could be withdrawn fromthe destruction process. In many cases, destruction of the cell becomespreventable as a result. Under favourable conditions, it is possiblethat a bridged cell recovers after a certain time and can again beaccommodated in the battery assembly.

Assuming that the activation of the protective apparatus takes placeearly enough, the cell to be bridged can even also supply the energy foractivating its protective apparatus. It can therefore act as an energystore of the protective apparatus before it is electrically removed fromthe battery assembly by means of bridging.

Depending on the present application, a protective apparatus accordingto the invention is equipped with an activation apparatus, which can beactivated by means of a signal which is generated within or outside ofthe protective apparatus. Which of these two options is to be preferredwill depend primarily on the nature of the activating event. It ispossible for example, that battery electronics monitor the cell voltageof individual cells and pass on the measurement results to a centralcontrol unit outside of the battery, which then for its part generatesthe signal for activating the protective apparatus of that cell or thosecells and forwards the same to the relevant protective apparatus orprotective apparatuses, which are assigned to the cells to be bridged.

A particularly advantageous embodiment of a protective apparatusaccording to the invention provides an activation apparatus which can beactivated by means of a signal which is generated by at least one sensorwhich measures at least one physical value which is indicative for theoperating state of the battery cell which is assigned to the protectiveapparatus. Such sensors can for example be temperature sensors which areattached to each cell and constantly measure the temperature of the cellassigned to them. Here also, various options for analysing themeasurement result are presented.

It is possible for example that a temperature sensor locally generates asignal for activating the protective apparatus of the cell, thetemperature of which it continuously measures. It is also possiblehowever, that a central control unit analyses the measurement results ofthese and/or other sensors, such as temperature and voltage sensors,together in order to generate a signal for activating the protectiveapparatuses of individual cells as a function of a plurality ofmeasurement results with the aid of a special decision logic, whichsignal is then forwarded to the activation apparatuses of the protectiveapparatuses of these cells and there leads to the activation of therelevant protective apparatuses.

According to a likewise preferred embodiment of the present invention, aprotective apparatus is provided, the activation apparatus of which canbe deactivated in the case of the subsequent cessation of theprerequisites for its activation, whereupon this protective apparatusreverses the bridging of the cell assigned thereto, as a result of whichthis cell is reintegrated into the battery assembly. The activationapparatus of the protective apparatus according to the invention canpreferably also be realised in such a manner that, for example followinga cooling of the relevant cell, the same can again be connected to thebattery assembly. The energy required for this can for example beremoved from the now again functional cell itself or the other cellsremaining in the battery assembly. In the case of this connection, theenergy store for activating the protective apparatus can preferably alsobe recharged.

According to a likewise preferred embodiment of the present invention, aprotective apparatus is provided, which is configured in such a mannerthat it can be arranged between the pole contacts of adjacent cells.FIGS. 3, 4, 8, 10 and 11 show illustrations of such exemplaryembodiments of the present invention.

According to a likewise preferred embodiment of the present invention, aprotective apparatus is provided with an activation apparatus, whichcomprises a fuse wire, which holds a wave spring, which serves as energystore, in a tensioned state, and which is activated by a current pulsewhich fuses the fuse wire, whereupon the wave spring is relaxed andprovides the energy required to change the interconnection. Thismechanical configuration of the energy store is to be produced—forexample, compared to an external active control of the activationapparatus—particularly robustly with respect to disturbances and—due toeliminated signal lines—inexpensively.

Also advantageous is a protective apparatus according to the inventionwith a housing closed in an airtight manner. A protective apparatusaccording to the invention, the housing of which is filled with an inertprotective gas, is particularly advantageous. Compared to a housingfilled with ambient air, the corrosion protection with a suitable choiceof the protective gas is often better.

FIG. 5 shows a battery cell 501 with a protective apparatus according tothe invention. The electrodes 503 and 504 are connected to contact rails509 by means of suitable contact plates 506 and 507. A wave spring 508changes the position of the contact plate 507 when the protectiveapparatus of the cell 501 is activated.

FIG. 6 shows an enlarged illustration of a protective apparatusaccording to the invention with the electrodes 603, 604, the wave spring608 and the contact plates 606 and 607. As FIG. 7 shows, the wave spring708 is mounted on a bearing 710, which ensures that, in the case offusing fuse wire 711, the relaxing wave spring cannot deflect downwards,for which reason, the contact plate 707 of the electrode 704 must pushupwards in the case of an activation of the protective apparatus.

As can be seen in FIG. 8, the contact plate 707 or 807 makes contactwith the contact plate 806 of the adjacent cell 802 before theactivation. Following activation by means of the fusing of the fuse wire811 it makes contact with the contact rail 805.

The side sectional illustrations of FIGS. 9 a, 9 b and 12 a and 12 bshow the same embodiment of the protective apparatus according to theinvention before and after the activation. The FIGS. 9 a and 12 a showthe context for the sections illustrated in the FIGS. 9 b and 12 b.

According to a preferred embodiment of the invention, an activationapparatus is provided for the protective apparatus according to theinvention, in which at least one component made up of a shape memorymaterial changes the interconnection by means of a change in the shapeof this component, as soon as and/or as long as the temperature of thiscomponent lies outside of a defined temperature range.

Various materials with shape memory are known. In the main, suchmaterials are metallic alloys, so-called shape memory alloys or plasticswith shape memory, which are also termed shape memory polymers. In thecase of the shape memory alloys, the shape change is based on atemperature-dependent lattice transformation of two different crystalstructures of a material. In this case, it imparts the high-temperaturephase, which is termed austenite, and the low-temperature phase, whichis also termed martensite, of the shape memory material. Both phases canblend into one another by means of a temperature change. In thiscontext, one also speaks of a two-way effect. This structuraltransformation is at least approximately independent of the rate oftemperature change. To initiate the desired phase change, the parametersof temperature and mechanical stress are often approximately equal, i.e.the transformation can be induced not only thermally but also often in astress-induced manner.

Shape memory alloys can convey quite large forces without materialfatigue in up to several hundred thousand movement cycles. Theirspecific working capacity, i.e. the ratio of work performed to thematerial volume exceeds the specific working capacity of many otherso-called actuator materials by far. In the applications of shape memoryalloys, a distinction is often made between the so-called one-way(memory) effect and the so-called two-way (memory) effect. In a one-wayeffect, a one-time shape change is to be observed during heating of amaterial sample previously pseudoplastically deformed in the martensiticstate. This one-way effect allows only a one-time shape change. Therenewed cooling causes no further shape change. For the use of shapememory alloys for actuator technology also, e.g. as a setting element,especially in connection with the present invention, it is oftendesirable, however, that the component can return to its martensitic“cold form” again.

There are basically two ways to bring about a shape reversion of thematerial:

a) The so-called external or extrinsic two-way effect.

-   -   In the case of the external two-way effect, the shape reversion        occurs during cooling of a component by means of an externally        acting force which forces the shape reversion. This can be        realised e.g. by means of a spring which was tensioned during        the heating of the shape memory material.        b) The so-called intrinsic two-way effect    -   Other shape memory alloys execute the shape reversion, but        without the action of external forces also. This process is also        termed the intrinsic two-way effect. Shape memory alloys of this        type can “remember” two shapes as it were—one at high and one at        low temperature in each case. The component made from a shape        memory material must have previously been “trained” by means of        thermomechanical treatment cycles so that it assumes its defined        shape again when cooling. Here, the formation of stress fields,        which promote the formation of certain martensite variants        during cooling, is effected in the material. The trained shape        for the cold state is therefore in one sense merely a preferred        shape of the martensite structure. The conversion of the shape        can only take place in the case of the intrinsic two-way effect        if no external forces act against it. Therefore, such a        component is therefore not in a position during cooling to carry        out work.

In the case of shape memory alloys, in addition to the usual elasticdeformation, a reversible shape change caused by the action of anexternal force can often be observed. This “elastic” deformation mayexceed the elasticity of conventional materials by up to twenty times.The cause of this material behaviour lies not in interatomicinteraction, however, but rather in a phase transformation within thematerial. Here, under external stresses, the so-called cubic facecentred austenite transforms into monoclinic martensite. Undermechanical relief, the martensite is transformed back into austenite. Asthe arrangement of atoms in the crystal structure is not changed hereand therefore each atom retains its adjacent atom, one also speaks of adiffusionless phase transformation. This material property is alsotermed pseudoplastic behaviour. The material returns to its originalshape when relieved due to its inner stress. Temperature changes are notrequired to this end.

Examples of shape memory alloys are alloys of nickel and titanium, ofcopper and zinc, of copper, zinc and aluminium, of copper, aluminium andnickel, and of iron, nickel and aluminium.

In addition to the metallic shape memory alloys, shape memory polymersform a second important group of shape memory materials. Shape memorypolymers are plastics which have a so-called shape memory effect, whichtherefore appear to be able to “remember” their earlier external shape,despite an interim strong deformation. Shape memory polymers whichbecame known early consisted of two components. The first was an elasticpolymer, a type of “spring element”, the second a hardening wax that the“spring element” can lock in any desired shape. If one heats the shapememory polymer, then the wax becomes soft and can no longer counteractthe force of the spring element. The shape memory polymer assumes itsoriginal shape.

As with the shape memory alloys, there are shape memory polymers whichassume their original shape again when heated. This behaviour is knownas the one-way memory effect, as in the case of the shape memory alloys.

More recently, polymers with a reversible shape memory effect have alsobecome known, which are controlled not thermally but often optically.Examples for this include so-called butyl acrylates which crosslink attheir side chains via cinnamic acid groups under ultraviolet light of acertain wavelength and dissolve the bond again when irradiated with adifferent wavelength. If one irradiates a component of this type on oneside, then a shape change of this material results by means of thecrosslinking initiating on one side. In the meantime, magneticallycontrollable shape memory polymers have also become known.

A preferred embodiment of the invention provides an electricallyconductive component made up of a shape memory material as a constituentof the activation apparatus. Electrically conductive shape memorymaterials can be used in different ways in connection with the presentinvention. In a first variant, the same current flows through theelectrically conductive component made up of the shape memory material,as also charges or discharges the galvanic cell to which the protectiveapparatus is assigned, which contains the activation apparatus, whichcontains the electrically conductive component made up of the shapememory material.

With an appropriate choice of materials, especially in the case of asuitable dimensioning of the temperature values at which the materialassumes one of two possible shapes in each case, it can be achieved inthis way with the aid of the electrically conductive component made upof a shape memory material that, when a certain value of the currentwhich is flowing through the component is exceeded, the device iscorrespondingly heated and that the component interrupts the current asa consequence.

Various variants for realising the present invention are in turnpossible within these variants. In a first variant, the shape memorymaterial component can be brought back to its original shape with theaid of an elastic spring, as soon as it has cooled down again afterturning off the current. In an implementation using two-way effect shapememory materials, it is also possible however, to effect the regressionof the shape without using an elastic spring, solely with the aid of thememory effect of the material.

Taking account of these conditions, it is very simply possible for theperson skilled in the art to produce protective apparatuses for galvaniccells on the basis of the present description with the aid of componentsmade up of shape memory alloys or shape memory polymers, which in thecase of an activation of the protective apparatus lead to a change ofthe interconnection by means of bridging, and which, depending on thecircumstances and objectives of the relevant application of thisbridging, also reverse the bridging again after the cessation ofcircumstances requiring the bridging, and therefore electricallyreintegrates the galvanic cell into the battery assembly.

Which of these options are implemented in each case by the personskilled in the art depends on the relatively narrow circumstances of theapplication considered in each case. If the bridge was used to prevent aparticularly critical situation, it will be appropriate in many cases tonot reverse the bridging, even after the cessation of the circumstancesrequiring the bridging. On the other hand, there are applications inwhich the bridging was triggered by circumstances which are suited bytheir nature to reversing the bridging again after the cessation ofthese circumstances. An example of such a situation may be present, if agalvanic cell was exposed to too high a temperature due to externalinfluences and therefore had to be bridged temporarily without thisbridging needing to be long-term, perhaps because the heating of thegalvanic cell would be an indication for an imminent destruction of thisgalvanic cell.

An activation apparatus with an electrically conductive component madeup of a shape memory material, through which the current, using whichthe cell assigned thereto is charged or discharged, flows, willtherefore be an advantageous embodiment of the present invention incases in which the component made up of the shape-memory material, isincluded itself in the contacting of the galvanic cell. If, by contrast,a design is intended, in which the component made up of the shape memorymaterial is not used for contacting the galvanic cell, then anotherembodiment of the invention, in which an electrically insulatingcomponent made up of a shape memory material is used, is suitable. Inthese cases it will often be advantageous if the component made up ofthe shape memory material, by means of the deformation thereof, performsthe work which is required to displace electrical conductive contactelements on the galvanic cell or within an arrangement of galvanic cellsin such a manner that the change according to the invention of theinterconnection is effected, which enables a bridging of the galvaniccell and thus the removal thereof from the battery assembly.

When using an electrically conductive component made up of a shapememory material, yet another design variant of the invention is inaddition possible, in which the current flows through this component,which current is controlled by a signal which is generated within andoutside of the protective apparatus for controlling the activationapparatus. A signal of this type for the activation can in turn begenerated by a sensor which measures a physical value which isindicative for the operating state of a galvanic cell which is assignedto the protective apparatus, because the activation apparatus includesthe component with the shape memory material.

To limit inrush currents during the reintegration of galvanic cellsremoved from a cell assembly into the cell assembly, NTC resistors canadvantageously be used to limit inrush currents. An NTC resistor of thistype, which can also be used as a contact element in connection withgalvanic cells according to the invention, is preferably cold before itis switched on; it therefore conducts poorly and reduces the inrushcurrent. After switching on, it warms up by means of the current flowand loses its high initial resistance. Particularly advantageously, suchNTC resistors can be used if they are short circuited following a shortperiod, for example after a few milliseconds, with the aid of anelectromechanical switch (relay), so that they can cool down. As aresult, the service life of the NTC resistors is increased and as afurther advantage, as the NTC resistors can cool down following theshort circuit by means of the relay, an immediate recovery of the NTCresistor results, even in the case of short switch-off periods.

NTC resistors or so-called resistors with a negative temperaturecoefficient (“negative temperature coefficient thermistors”), which arealso termed NTC thermistors, are electrically conductive materials whichconduct electricity better at high temperatures than at lowtemperatures. Thus, the electrical resistance thereof decreases withincreasing temperature. Therefore, one also speaks of a negativetemperature coefficient.

Pure semiconductor materials and various other alloys with negativetemperature coefficients show heat-conducting behaviour. Components forwhich the temperature-dependent behaviour specifically is utilised, areoften metal oxides which are pressed, sintered and mixed with binders.The resistance of components of this type can be set in a wide range bymeans of the mixing ratio of various materials.

NTC resistors are often produced from a mixture of semiconducting metaloxides or from so-called compound semiconductors. These include inparticular oxides of manganese, nickel, cobalt, iron, copper or alsotitanium.

So-called PTC resistors, which are also termed PTC thermistors show theopposite behaviour compared to NTC resistors. The abbreviation PTC herestands for the positive temperature coefficients of these materials. Oneis concerned here with current-conducting materials, which can betterconduct the current at low temperatures than at high temperatures.Basically, although all metals have a positive temperature coefficient,in contrast with the PTC resistors meant here, the temperaturecoefficient of the usual metals is generally substantially smaller andbehaves linearly for the most part. PTC resistors of this type can forexample be used in connection with the here-described galvanic cellsaccording to the invention to stabilise the temperature of a galvaniccell. Namely, if the temperature of an individual galvanic cellincreases, then by means of suitable arrangement of a PTC resistor ofthis type, it can be achieved that the temperature thereof alsoincreases and therefore the resistance of this PTC resistor componentrises. As the conductivity thereof decreases with increasingtemperature, the current loading of the correspondingly connectedelectrochemical energy store, that is to say of the galvanic cell, isreduced, which in many cases will lead to this galvanic cell coolingdown.

Following the cooling down of the galvanic cell, a PTC resistor locatedin the vicinity thereof will also cool down, whereupon its conductingcapability rises again. As a consequence, the current can rise again bymeans of this PTC resistor. PTC resistors can therefore be used in thecontext of the present invention to limit the current into a galvaniccell during charging or out of a galvanic cell during discharging andtherefore to keep the temperature of this galvanic cell stable.

Further advantageous embodiments of protective apparatuses according tothe invention can be realised by means of a clever combination of NTCresistors, PTC resistors and shape memory materials. In the case of asuitable design combination of NTC resistor or PTC resistor materialswith shape memory materials, it can be achieved that not only theelectrical conductivity of a contact element used for contacting a cellin a cell assembly, that is to say its electrical resistance, changes,but rather it can additionally be achieved that in the case of theachievement of certain temperatures or in the case of leaving certaintemperature ranges, a shape change of the corresponding component takesplace, which leads to a switching or to a change of the interconnectionof the galvanic cells.

The following reference numbers were used in the figures for identifyingthe illustrated details:

-   -   201, 301, 801, 1001, 1101, 1201    -   Galvanic cell, battery cell    -   202, 302, 802, 1002, 1102, 1202    -   Galvanic cell, battery cell    -   203, 503, 603, 803, 1003, 1103, 1203    -   Electrode, diverter, diverter plate    -   204, 504, 604, 704, 1104    -   Electrode, diverter, diverter plate    -   205, 405, 805, 905, 1005, 1205    -   Contact rail, contact element    -   206, 406, 506, 606, 706, 806, 1106    -   Contact plate of an electrode    -   207, 407, 507, 607, 707, 807, 907, 1007, 1107, 1207    -   Contact plate of an electrode    -   208, 408, 508, 608, 708, 808, 908, 1008, 1108, 1208    -   Wave spring    -   209, 409, 509, 709, 1009    -   Contact rail, contact element    -   910, 1110, 1210    -   Bearing of the wave spring    -   911, 1011, 1111, 1211    -   Fuse wire    -   212, 1012, 1212    -   Contact rail, contact element    -   1013    -   Contact plate of an electrode    -   214, 1014    -   Contact plate of an electrode    -   1230    -   Predetermined breaking point of the fuse wire    -   390    -   Section from FIG. 3 illustrated in FIG. 4

The FIGS. 2, 3, 4, 8, 10 and 11 show exemplary embodiments of a batterymade up of battery cells with protective apparatuses according to theinvention. A battery of this type preferably consists of a plurality ofprotective apparatuses which are arranged between adjacent cells of thebattery. In this case, a plurality of contact elements is provided forinterconnecting a series connection and/or parallel connections of cellsof the battery. A first part of these contact elements is arranged in amovable manner; a second part of these contact elements is arranged inan immovable manner. An activation of a protective apparatus of a firstcell causes a movable first contact element, which is used before theactivation for an electric series connection to an adjacent second cell,is moved in the case of activation of the protective apparatus andpressed against an immovable second contact element, as a result ofwhich the first cell is bridged and therefore electrically removed fromthe series connection.

1-17. (canceled)
 18. A protective apparatus for galvanic cells which areinterconnected by contact elements to form a battery, the contactelements being connected to pole connections of the battery cells,wherein the protective apparatus has an activation apparatus to activatethe protective apparatus, and the protective apparatus bridges a cellassigned to it by a change of interconnection when the protectiveapparatus is activated, the change in interconnection electricallyremoving the cell that is bridged from the battery assembly, and whereinan activation apparatus in which a current flows through and heats acomponent made of a shape memory material, which changes theinterconnection by means of a change in the shape of the component, aslong as the temperature of the component is outside of a predefinedtemperature range.
 19. The protective apparatus according to claim 18,wherein the component made up of a shape memory material is anelectrically conductive component or an electrically insulatingcomponent.
 20. The protective apparatus according to claim 19, whereinthe current from a cell assigned to the protective apparatus is chargedor discharged, or the current controlled by a signal which is generatedwithin or outside of the protective apparatus for controlling theactivation apparatus, flows through the electrically conductivecomponent made up of a shape memory component.
 21. The protectiveapparatus according to claim 18, comprising: an energy store to storeenergy required to change the interconnection, the energy storeproviding the energy to change the interconnection in the case of anactivation.
 22. The protective apparatus according to claim 21,comprising a mechanical energy store.
 23. The protective apparatusaccording to claim 18, wherein the protective apparatus is assigned toindividual cells of a battery.
 24. The protective apparatus accordingclaim 18, comprising: an activation apparatus to be activated by asignal generated outside of the protective apparatus and/or a signalgenerated inside the protective apparatus.
 25. The protective apparatusaccording claim 18, comprising an activation apparatus to be activatedby a signal generated by at least one sensor which measures at least onephysical value indicative of an operating state of a galvanic cellassigned to the protective apparatus.
 26. The protective apparatusaccording to claim 24, wherein the activation apparatus is deactivatedupon a subsequent cessation of prerequisites for its activation, and theprotective apparatus reverses the bridging of the cell assigned theretoto reintegrate the cell into the battery assembly.
 27. The protectiveapparatus according to claim 18, wherein the protective apparatus isconfigured to be arranged between pole connections of adjacent cells.28. The protective apparatus according claim 18, comprising: anactivation apparatus including a fuse wire, which holds a wave springthat serves as energy store, in a tensioned state, the activationapparatus being activated by a current pulse which fuses the fuse wire,wherein the wave spring is relaxed and provides the energy required tochange the interconnection in response to fusion of the fuse wire. 29.The protective apparatus according to claim 18, comprising an airtighthousing.
 30. The protective apparatus according to claim 29, wherein theairtight housing is filled with a protective gas.
 31. A galvanic cellwith a protective apparatus according to claim
 17. 32. A battery with atleast one galvanic cell according to claim
 31. 33. A battery with aplurality of galvanic cells according to claim 30, wherein the batteryincludes a plurality of protective apparatuses arranged between adjacentgalvanic cells of the battery; a plurality of contact elements tointerconnect a series connection of galvanic cells of the battery, afirst part of the plurality of contact elements being movable, a secondpart of the plurality of contact elements being immovable, wherein anactivation of a protective apparatus of a first galvanic cell causes amovable first contact element, which is used before the activation foran electric series connection to an adjacent second galvanic cell, ismoved in the case of activation of the protective apparatus and pressedagainst an immovable second contact element to bridge the first galvaniccell and electrically remove the first galvanic cell from the seriesconnection.